Effects of Weaning by Surrogate Mothers (ACI) on Tumor Development in SD Rats Treatedwith Methylnitrosourea (MNU) and/or N-Methyl-N-nitro-N-nitrosoguanidine (MNNG)

In this experiment, MNU was administered, followed by MNNG, to assess effects ofsurrogate mothering on tumor. One or two day old male SD pups were treated with or without30mg/kg body weight of methylnitrosourea (MNU) and nursed by SD or ACI surrogate mothersfor 5 weeks. When 6-weeks-old they were then treated with 100ppmN-methyl-N-nitro-N-nitrosoguanidine (MNNG) or tap water for 16 weeks. The tumor incidencein the MNNG alone group was significantly lower than with MNU alone or MNU+MNNG (p<0.01).Kidney or nerve tumors mainly developed in the MNU group, gastric tumors in the MNNG group,and the two combined in the MNU+MNNG group. The incidence and mean number of tumors didnot significantly differ between the two weaning groups. However, mean survival time withthe ACI surrogate mothers after treatment with MNU was increased as compared with the SDmother group. Cumulative development of tumors in the ACI surrogate mother group was alsodelayed (p<0.05). Similar results were obtained with MNU+MNNG and MNNG alone. The presentexperiment suggested that tumor induction might be effected by components of the mother'smilk.